Device for damping vibration in a cable

ABSTRACT

The device includes a first member surrounding and secured to a section of a cable, a second member connected to an element to which a portion of the cable is attached, and arranged around said first member, a resilient or viscoelastic ring engaging the first member and the second member, and a flexible container housed in a ring-shaped compartment between the two members and filled with a viscous substance.

BACKGROUND OF THE INVENTION

The present invention concerns a device for damping vibration in acable. It has particular but not exclusive application in the field ofcivil engineering works with a structure using such cables, for examplesuspension or cable-stayed bridges.

These cables or stays are subjected to vibration caused by the windand/or the rain or else by vehicle traffic on the bridge.

The invention concerns more exactly a device including a first membersurrounding and secured to a section of the cable, a second member,connected to an element to which a cable portion is attached, andarranged around the first member, and damping means arranged between thefirst and second members.

A device of this type, for damping vibration in a stay, is described inEuropean patent 0 343 054. In the damping device presented in thisdocument, the two members delimit a ring-shaped cavity filled with aviscous substance providing the required damping during relative motionsof the two members.

This former device has good performance in terms of damping. It has thefurther advantage of being relatively compact and of not beingdetrimental to the aesthetic quality of the structure. However, ensuringa seal between the ring-shaped cavity and the exterior can be tricky. Aset of joints has to be set in place, which limits the reliability ofthe device and complicates its installation. On the other hand, thedevelopment of a particular device requires a special design of the twomembers and appropriate sealing means, with this design having to bere-conceived each time, for example, that changes are made to the staydimensions or to the required dynamic properties.

One object of the present invention is to propose a damping device for atensioned cable, as a straightforward and reliable response to problemsof sealing, the achievement of which is facilitated.

SUMMARY OF THE INVENTION

The invention thus proposes a damping device of the type mentioned inthe introduction, in which damping means include on the one hand aresilient or visco-elastic ring engaging the first member and the secondmember, on the other hand a flexible container containing a viscoussubstance, this flexible container being housed in a ring-shapedcompartment formed between the first and second members.

The flexible container constitutes a constant volume damping chamberwhich can be easily sealed. Cable vibration is effectively attenuatedthrough the combined effect of the resilient or visco-elastic ring andthe viscous damping provided by the substance contained in the flexiblecontainer. Dissipation of vibrational energy results from the movementsof the viscous substance in the flexible container, prompted when thecable vibrates relative to the element to which it is attached.

In a preferred version, the flexible container consists of a hose coiledin the ring-shaped compartment. It is thus possible to adapt todifferent dimensions of the cable or stay to be damped, simply byadjusting the length of the hose.

To facilitate the installation of the device, the resilient orvisco-elastic ring may be composed of two parts of generallysemi-cylindrical shape which can be attached to each other by means ofpins approximately parallel to the cable section, of assembly bolts orelse of a tightening belt.

To advantage, each of these parts comprises several metal half-bushingssunk into a resilient or moulded visco-elastic material, thehalf-bushing ends protruding from the moulded material and beingprovided respectively with assembly means such as pinning apertures.

In a version of this latter type, each of the parts comprises two outerhalf-bushings of the same diameter, located on either side, an innerhalf-bushing of smaller diameter relative to the cable sectiondirection. It is then the flexibility of the resilient or visco-elasticmaterial between the inner half-bushing and the outer half-bushingswhich enables the relative motion of the cable section relative to thesecond member, while exerting return force towards the normal position.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows diagrammatically how a device in accordance with theinvention is placed near the anchored end of a stay;

FIG. 2 is an axial sectional view of a device in accordance with theinvention;

FIG. 3 is a cross sectional view, along the plane III—III shown in FIG.2, of an inner the of the device, and showing additionally the sectionalplane II—II of FIG. 2;

FIG. 4 is a perspective view of a moulded part forming half of aresilient ring of the device shown in FIG. 2; and

FIG. 5 is an axial sectional view of another version example of a devicein accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows diagrammatically the place where a damping device may beplaced in accordance with the invention on the stay 6 of a structure 8such as a cable-stayed bridge.

In a known way, the stay is anchored at its two ends on respectiveblocks 10 integral with appropriate footings and structure elements 12.In the example shown in FIG. 1, the damping device is placed near thelower end 14 of the stay 6, anchored in the apron 12 of the bridge. Itwill be understood that a similar structure may be placed near the upperend of the stay 6, anchored in a bridge tower.

The end 14 of the stay passes into a rigid tubular guide 16 fixed to theanchoring block 10.

The damping device, which is shown very diagrammatically in FIG. 1 andin more detail in FIG. 2, comprises:

an inner tube 20 into which passes a stay section 6, and fixed to thissection;

an outer tube 22 placed around the inner tube 20;

a resilient or visco-elastic ring 24 one inner face of which issupported against the inner tube 20 and an outer face is supportedagainst the outer tube 22;

a flexible container such as a hose 26 containing a viscous substance28.

In the example in FIG. 2, this container 26 is housed in a ring-shapedcompartment 30 delimited on the one hand by a ring-shaped groove 32 witha V-shaped cross section present on one face of the resilient ring 24,and on the other hand by one of the tubes 20, 22 (the outer tube 22 inthe example shown).

FIGS. 2 and 3 show a possible assembly of the inner tube 20 on the stay6 in the case where the latter is composed of strands collected into abundle of hexagonal cross section. The tube 20 consists of twosemi-cylindrical portions 20 a, 20 b each belonging to a respectivebush. Each of the bushes includes three plates 34 which are appliedagainst the sides of the hexagonal section of the stay, withinterposition of a strip of adhesive 36. Longitudinal wedges 38 arewelded between the semi-cylindrical portion 20 a and the plates 34, atthe centre of the latter. As is shown in FIG. 1, the plates 34 have twoaxial ends which protrude from the tube 20. At these ends, the twobushes comprise lateral edges 40 enabling their assembly by means ofscrews 42. The tightening of the screws 42 enables the tube 20 to belocked on the stay 6 section.

The outer tube 22 is presented as a cylindrical casing which, in use, isattached to the tubular guide 16 anchored to the footing. In theassembly example shown in FIG. 1, the outer tube 22 has towards thelower end of the stay a flange 46 bolted on an additional flange 48provided at the outlet of the tubular guide 16.

In order to facilitate its installation on the stay, the resilient ring24 is constituted in two halves of generally semi-cylindrical shapeassembled after their installation on the inner tube 20.

Such a half-ring 50 is shown in FIG. 4. It is composed of three metalhalf-bushings 52, 54, 56 sunk by moulding into an elastomer material 58,namely two outer half-bushings of the same diameter 52, 54 and an innerhalf-bushing of smaller diameter 56. In a radial plane, the elastomermaterial 58 has a generally V-shaped cross section, the innerhalf-bushing 56 being located at the base of this V, and the two outerhalf-bushings 52, 54 being located at the ends of the branches of thisV. The groove 32 is thus determined between the two branches of the Vconstituted of elastomer material capable of compression under thestress of transverse vibration of the stay 6.

As is shown by the upper part of FIG. 2 and the partial stripping of theelastomer material 58 in FIG. 4, the metal half-bushings 52, 54, 56 eachhave, over most of their perimeter, a rectangular shaped cross section.To allow the assembly of the two halves 50, the half-bushings 53, 54, 56each have their two ends 62, 64, 66 which protrude from the mouldedelastomer material 58. One end 62, 64, 66 of each half-bushing 52, 54,56 is in the shape of a clevis provided with a pinning aperture 72, 74,76, whereas the other end 63, 65, 67 has a complementary shape of theclevis and is provided with a corresponding pinning aperture 73, 75, 77.The pinning apertures 72-77 allow the assembly of the two ring halves 50by means of three pairs of pins 82, 84, 86 extending parallel to thedirection of the stay section 6 (see the lower part of FIG. 2).

A ring half 50 is easily manufactured by injecting the elastomermaterial 58 into an appropriately shaped mould in which have previouslybeen placed the three half-bushings 52, 54, 56, then by vulcanising theelastomer material. The stiffness of the resilient ring 24 may beadjusted in accordance with the required dynamic properties by workingon the elasticity parameters and levels of thickness of the resilient ormoulded visco-elastic material.

In the device in FIG. 2, the flexible hose 26 is coiled in a helix inthe compartment 30 delimited on the one hand by the groove 32 of thering 24, and on the other hand by the inner face of the outer tube 22.The hose 26 has one of its ends closed, and its other end whichcommunicates with the outside of the compartment 30 by means of a bore90 arranged in a drift pin 84 of one of the pairs of outer half-bushings54 of the resilient ring 24. This end 92 of the hose 26 is thusaccessible to fill the latter with the viscous damping substance. Thissubstance 28 is typically an oil or another viscous fluid, or a viscousgel the viscosity of which is optimised as a function of thecharacteristics of the stay to be damped.

The installation of the damping device described above is carried outfor example in the following way. The strands of the stay 6 areinstalled and anchored at their two ends, by passing them through thetubular guide 16 and the outer tube 22. The tube 22 is then separatedfrom the guide 16 so as to give access to the stay section receiving thedevice. The inner tube 20 is installed and locked on the stay section byassembling its two bushes and by tightening the screws 42. The twohalves of the ring 24 are then installed around the inner tube 20, thenpinned. After coiling the flexible hose 26 in the groove 32, the outertube 22 is engaged around the whole, the hose 26 is filed with oil 28,and the outer tube 22 is attached to the flange 48 of the tubular guide16. When the strand 6 comprises an outer protective casing, the lattermay be attached on the end of the outer tube 22 opposite the guide 16.

FIG. 5 shows a version variant of the invention, in which the ring 24and the ring-shaped compartment where the flexible container is housedare juxtaposed along the direction of the stay 6 section. The inner tubeis divided into two juxtaposed sections 100, 101 attached to the stay inthe manner described by reference to FIG. 3. One of these sections 100receives the ring 24 which has the same structure and the same mode ofassembly as previously (FIG. 4), except that the groove 32 is not usedfor containing the viscous substance container.

The other section 101 of the inner tube is provided with two transverseflanges 103, 104 at its axial ends. The ring-shaped compartment 105,receiving the flexible container 106 of viscous material 28, isdelimited internally by the inner tube section 101, and axially by thetwo flanges 103, 104. Outwards, this compartment 105 is delimited by abushing 107 acting as a piston. This bushing 107 is presented in theform of two half-bushings assembled around the stay during theinstallation of the device. Outwards, the half-bushings have radialprotrusions 108 by which they rest on the outer tube 22.

In the version in FIG. 5, the flexible container 106 consists of apocket occupying the axial length of the ring-shaped compartment 105 andencasing the perimeter of the tube section 101. This pocket 106 isfilled with viscous substance 28 after installation of the unit viaconduits 109 passing through the bushing 107 and its protrusions 108 asshown in FIG. 5. In use, vibration in the stay results in thepiston-bushing 107 being moved radially relative to the tube section 101and to the flanges 103, 104 so that the substance contained in thepocket 106 moves within a constant volume chamber and provides thedamping required.

Although the invention has been described by reference to particularversion examples, it will be understood that various variants may beprovided to these examples without departing from the context of thepresent invention. Thus, a device in accordance with the invention maybe used to damp vibration in a cable other than a stay, for example atrack cable or a suspension bridge hanger or again a submarine cableetc. The cable portion attached to a footing or the like is notnecessarily one of its ends. On the other hand the element to which thisportion is attached may be a footing or any structure element, includinga cable network.

What is claimed is:
 1. A device for damping vibration in a tensionedcable, comprising: a first member surrounding and secured to a sectionof the cable; a second member arranged around the first member with aspace therebetween, and connected to an element to which a portion ofthe cable is attached; and damping means arranged in the space betweenthe first and second members, wherein the damping means comprise aresilient or visco-elastic ring engaging the first member and the secondmember, and a flexible container containing a viscous substance, saidflexible container being housed in a ring-shaped compartment formed inthe space between the first and second members, and said flexiblecontainer comprising a hose coiled in the ring-shaped compartment.
 2. Adevice according to claim 1, wherein the resilient or visco-elastic ringis composed of two parts of generally semi-cylindrical shape.
 3. Adevice according to claim 2, wherein the two parts of generallysemi-cylindrical shape are attached to each other by means of pinsapproximately parallel to the cable section.
 4. A device according toclaim 3, wherein the resilient or visco-elastic ring has a groove which,with one of the members delimits the ring-shaped compartment, andwherein one of the pins comprises an axial bore giving access toflexible container for filing the container.
 5. A device according toclaim 2, wherein each of the two parts of generally semi-cylindricalshape comprises several metal half-bushings sunk into a mouldedresilient or visco-elastic material, the ends of the half-bushingsprotruding from the moulded material and being respectively providedwith assembly means.
 6. A device according to claim 5, wherein each ofthe parts of generally semi-cylindrical shape comprises two outerhalf-bushings having a first diameter, located on either side of aninner half-bushing having a second diameter smaller than said firstdiameter relative to the direction of the cable section, wherebyflexibility of the resilient or visco-elastic material between the innerhalf-bushing and the outer half-bushings permits a relative motion ofthe cable section relative to the second member.
 7. A device accordingto claim 1, wherein the resilient of visco-elastic ring has a groovewhich, with one of the members delimits the ring-shaped compartment. 8.A device according to claim 1, wherein the resilient or visco-elasticring and the ring-shaped compartment where the flexible container ishoused are juxtaposed along the direction of the cable section.
 9. Adevice according to claim 8, wherein the ring-shaped compartment isdelimited internally by the first member, axially by two transverseflanges integral with the first member, and externally by a bushingresting on the second member and movable radially between the flangesrelative to the first member.
 10. A device for damping vibration in atensioned cable, comprising: a first member surrounding and secured to asection of the cable, a second member arranged around the first memberwith a space therebetween, and connected to an element to which aportion of the cable is attached; and damping means arranged in thespace between the first and second members, wherein the damping meanscomprise a resilient or visco-elastic ring engaging the first member andthe second member, and a flexible container a viscous substance, saidflexible container being housed in a ring-shaped compartment formed inthe space between the first and second members, the resilient orvisco-elastic ring is composed of two parts of generallysemi-cylindrical shape, the two parts of generally semi-cylindricalshape are attached to each other by means of pins substantially parallelto the cable section.
 11. A device according to claim 10, wherein theresilient or visco-elastic ring has a groove which, with one of the saidmembers, delimits the said ring-shaped compartment.
 12. A deviceaccording to claim 10, wherein the resilient or visco-elastic ring has agroove which, with one of said members delimits said ring-shapedcompartment, and wherein one of the pins comprises an axial bore givingaccess to the flexible container for filling said container.
 13. Adevice according to claim 10, wherein the resilient or visco-elasticring and the ring-shaped compartment where the flexible container ishoused are juxtaposed along the direction of the cable section.
 14. Adevice according to claim 13, wherein the ring-shaped compartment isdelimited internally by the first member, axially by two transverseflanges integral with the first member, and externally by a bushingresting on the second member and movable radially between flangesrelative to the first member.
 15. A device according to claim 10,wherein each of the parts of generally semi-cylindrical shaped comprisesseveral metal half-bushings sunk into a moulded resilient orvisco-elastic material, the ends of the half-bushings protruding fromthe moulded material and being respectively provided with assemblymeans.
 16. A device according to claim 15, wherein each of the parts ofgenerally semi-cylindrical shape comprises two outer half-bushingshaving a first diameter, located on either side of an inner half-bushinghaving a second diameter smaller than said first diameter relative tothe direction of the cable section, whereby flexibility of the resilientor visco-elastic material between the inner half-bushing and the outerhalf-bushings permits a relative motion of the cable section relative tothe second member.
 17. A device for damping vibration in a tensionedcable, comprising: a first member surrounding and secured to a sectionof the cable, a second member arranged around the first member with aspace therebetween, and connected to an element to which a portion ofthe cable is attached; and damping means arranged in the space betweenthe first and second members, wherein the damping means comprise aresilient or visco-elastic ring engaging the first member and the secondmember, and a flexible container containing a viscous substance, saidflexible container being housed in a ring-shaped compartment formed inthe space between the first and second members, the resilient orvisco-elastic ring is composed of two parts of generallysemi-cylindrical shape, and each of the parts of generallysemi-cylindrical shape comprises several metal half-bushings sunk into amoulded resilient or visco-elastic material, the ends of thehalf-bushings protruding from the moulded material and beingrespectively provided with assembly means.
 18. A device according toclaim 17, wherein each of the parts of generally semi-cylindrical shapecomprises two outer half-bushings having a first diameter, located oneither side of an inner half-bushing having a second diameter smallerthan said first diameter relative to the direction of the cable section,whereby flexibility of the resilient or visco-elastic material betweenthe inner half-bushing and the outer half-bushings permits a relativemotion of the cable section relative to the second member.
 19. A deviceaccording to claim 17, wherein the resilient or visco-elastic ring has agroove which, with one of the said members, delimits the saidring-shaped compartment.
 20. A device according to claim 17, wherein theresilient or visco-elastic ring and the ring-shaped compartment wherethe flexible container is housed are juxtaposed along the direction ofthe cable section.
 21. A device according to claim 20, wherein thering-shaped compartment is delimited internally by the first member,axially by two transverse flanges integral with the first member, andexternally by a bushing resting on the second member and movableradially between the flanges relative to the first member.
 22. A devicefor damping vibration in a tensioned cable, comprising: a first membersurrounding and secured to a section of the cable, a second memberarranged around the first member with a space therebetween, andconnected to an element to which a portion of the cable is attached; anddamping means arranged in the space between the first and secondmembers, wherein the damping means comprise a resilient or visco-elasticring engaging the first member and the second member, and a flexiblecontainer containing a viscous substance, said flexible container beinghoused in a ring-shaped compartment formed in the space between thefirst and second members, and the resilient or visco-elastic ring has agroove which, with one of the said members, delimits the saidring-shaped compartment.
 23. A device according to claim 22, wherein theresilient or visco-elastic ring and the ring-shaped compartment wherethe flexible container is housed are juxtaposed along the direction ofthe cable section.
 24. A device according to claim 23, wherein thering-shaped compartment is delimited internally by the first member,axially by two transverse flanges integral with the first member, andexternally by a bushing resting on the second member and movableradially between the flanges relative to the first member.
 25. A devicefor damping vibration in a tensioned cable, comprising: a first membersurrounding and secured to a section of the cable, a second memberarranged around the first member with a space therebetween, andconnected to an element to which a portion of the cable is attached; anddamping means arranged in the space between the first and secondmembers, wherein the damping means comprise a resilient or visco-elasticring engaging the first member and the second member, and a flexiblecontainer containing a viscous substance, said flexible container beinghoused in a ring-shaped compartment formed in the space between thefirst and second members, the resilient or visco-elastic ring and thering-shaped compartment where the flexible container is housed arejuxtaposed along the direction of the cable section, and the ring-shapedcompartment is delimited internally by the first member, axially by twotransverse flanges integral with the first member, and externally by abushing resting on the second member and movable radially between theflanges relative to the first member.